High Idle on 5.7 Volvo Penta

[Hughes179]

I know this topic has been approached a number of times but most of the threads are hit a miss. I was headed into the dock last week when my engine all of a sudden idled up on its own to around 1200-1500 rpms. I’m running the 5.7 Volvo Penta GXi in my 2006 Four Winn’s Horizon 260 with around 300 hours. Engine had been running strong with no issues, good temp, oil pressure, and fuel.

Ultimately had to drift back into
dock to avoid a high idle shift so i didnt tear up my lower drive. I have some basic mechanical knowledge and assumed that based on the high idle and loud airy sound I probably had a air/fuel issue or busted vaccume Line. Checked all vaccume lines and everything looked good.

I ultimately had to run a hose to motor and start it at high idle back at home to trace the vaccume sound. Ended up determining it was sucking air right at the Idle air control port just inside the throttle body. I determined the IAC was fully retracted causing the idle to run up.

Pulled the IAC and noted it was not too dirty. I know I probably shouldn’t have manually moved the plunger but I did pull it out just enough to close off the intake port on the throttle body. Reinstalled it, but did not plug the power back in. Engine started and ran fine. With engine running I plugged the power back into the IAC. The plunger immediately retracted again and ran the idle back up.

To eliminate a faulty IAC I ordered a new one, which came in yesterday. Installed the new IAC with same outcomes. The plunger continued to retract. Just out of curiosity I reinstalled the old IAC with plunger out so I could run the engine at normal idle. I then plugged the new IAC in and determined the plunger was moving back and forth looking for that perfect position. So I assume the computer is working.

I read somehere that upon installed a new IAC the computer has to work for a while to learn the new sensor which may cause the engine to run at high idle until it warms up. Is this true? Furthermore I ran the engine with old IAC until it was 175ish.

I have not checked my fuel pressure, yet the fuel pump is newer and does not appear to be OEM. I assume the issue is engine side of IAC and not pre-throttle body side. Should I be looking at MAP, TPS, or knock sensors? Should I pull throttle body and give all the ports a good cleaning? Can I safely run the engine after manually positioning the plunger and leaving it unplugged as long as I don’t have cold start up problems? Most marine shops around the Dallas Fort Worth area are 5 weeks out and I don’t care to let my boat sit in shop the rest of the boating season for something that is holefully simple fix.

Any hell would be greatly appreciated. Thanks

 

[alldodge]

Really need to read codes

Faster idle can be from the TPS sending the wrong voltage to the ECM. It has 3 wires on it, 5V, Gnd and Reference. Should be a Orange/Blue wire which supplies reference to the ECM. At idle this voltage should be near zero (0.5V)

 

[CrozzCraft]

I know this post is a few years old, but my 2004 5.7 GXi is having the exact same issue. Like I wrote that myself. I read about this being a problem, but so far I haven’t read of reason of the problem or the solution.
I replaced the IAC and no change. Boat is idling in the 1200-1400 RPM range, and it was an all of the sudden issue which happened at some point on a 1 hr trip up LOTO, and when we slowed to dock, it wouldn’t settle down. It’s also the first time I noticed the sucking sound coming from the throttle body, which I traced to the air channel leading to the IAC on top of throttle body, just under the flame arrester.
We rand the boat for 2-3hrs the day before, with no issues. 1st time we’ve had her out this season.
I can put my finger over the air channel and the engine immediately slows to a normal idle, so it’s definitely an IAC issue, but it’s almost like the ECM and IAC are not communicating properly…any info or knowledge on this would be great. I had it to my local marina informally just to get their opinion, but they are primarily a Mercury shop and dont know the ins and outs of Volvo-Penta engines.
I added a video of the highl

 

[Fowler200]

I know this post is a few years old, but my 2004 5.7 GXi is having the exact same issue. Like I wrote that myself. I read about this being a problem, but so far I haven’t read of reason of the problem or the solution.
I replaced the IAC and no change. Boat is idling in the 1200-1400 RPM range, and it was an all of the sudden issue which happened at some point on a 1 hr trip up LOTO, and when we slowed to dock, it wouldn’t settle down. It’s also the first time I noticed the sucking sound coming from the throttle body, which I traced to the air channel leading to the IAC on top of throttle body, just under the flame arrester.
We rand the boat for 2-3hrs the day before, with no issues. 1st time we’ve had her out this season.
I can put my finger over the air channel and the engine immediately slows to a normal idle, so it’s definitely an IAC issue, but it’s almost like the ECM and IAC are not communicating properly…any info or knowledge on this would be great. I had it to my local marina informally just to get their opinion, but they are primarily a Mercury shop and dont know the ins and outs of Volvo-Penta engines.
I added a video of the highl

Any update on this issue? I’m having same problem on my 2005 5.7 GI